Gravity water filtration devices for outdoor adventure have been on the market for years. Popular for transportation in backpacks are devices that comprise a flexible collapsible container for being attached to a tree and having connected a tube at its lower end for driving water through a purification unit by gravity. Some models have a purification unit inside the flexible container and others have it outside the flexible container as part of the tube.
Examples of such bags and other gravity filters are disclosed in U.S. Pat. Nos. 2,792,942; 3,715,035; 4,828,698; 5,126,044; 5,332,495.
Due to market demands, improvements are made on a steady basis, especially because even minor advantages of products with respect to handling and safety have important competitive impact. Thus, there is an ongoing need for improvements, especially, with respect to safety, durability, and versatility in use.